Question

what mannerist conventions did parmigianino use in madonna with the long neck?
a composition that is simplified and symmetrical
figures that appear flattened and distanced from the viewer
distorted proportion and a complex composition
realistic anatomy and a simple background

Explanation:

Mannerism often features distorted proportions (like the elongated neck in Madonna with the Long Neck) and complex compositions. Simplified/symmetrical compositions (common in earlier Renaissance), flattened/distanced figures (not a key Mannerist trait), and realistic anatomy (more Renaissance) are not typical Mannerist conventions.

Answer:

distorted proportion and a complex composition